This application is a submission under 35 U.S.C. xc2xa7 371 and claims priority to Patent Cooperation Treaty Application Serial No. PCT/US00/28077, entitled PROCESS FOR THE METALLURGICAL TREATMENT OF MOLTEN STEEL IN A CONVERTER WITH OXYGEN TOP BLOWN ONTO THE MOLTEN STEEL AND AN OXYGEN BLOWING LANCE, filed Oct. 6, 2000, which application claims priority to German Patent Application Serial No. 199 48 187.3, entitled PROCESS FOR THE METALLURGICAL TREATMENT OF MOLTEN STEEL IN A CONVERTER WITH OXYGEN TOP BLOWN ONTO THE MOLTEN STEEL AND AN OXYGEN BLOWING LANCE, filed Oct. 6, 1999.
For the metallurgical treatment of molten steel in a converter, oxygen is blown onto the top of the molten steel under the control of a blowing lance. The oxygen lance is subjected to a high thermal load during this top blowing, particularly on its front end. It is therefore typical to cool the lance down intensively. The most effective way to cool an oxygen blowing lance is to thoroughly flush die head of the lance with a large volume of cool water under high pressure. The head of the lance is made of a material with good thermal conductivity, such as copper. High temperature peaks up to 3000 degrees C., particularly at the front end of the lance head which is the focus of heat radiating from the surface of the bath as well as wear and tear lead over time to a reduction in the thickness of the cooling chamber walls found in the head of the lance. If there is not enough distance between the head of the lance and the molten metal, the walls can weaken rapidly and suddenly rupture because they have been weakened. Any release of water vaporizes explosively and damages more than just the metallurgical process. If the lance head ruptures, the treatment of the enamel must also be terminated immediately.
To avoid the danger of a water release while simultaneously cooling the lance even when the lance is plunged into the molten steel melt, there is a process (DE 35 43 836 C2), which employs two blowing lances used in rotation. These two lances are cooled alternately and intensively with cool air and then with cool water. The lance in the blow position which is being plunged into the molten steel is cooled with cool air while the other lance outside of the molten steel is cooled intensively with cool water. By repeatedly switching as needed between cool air cooling and cool water cooling the overheating of either lance can be avoided, the advantage of effectively avoiding a water release is the cost of purchasing a second lance.
Starting at this point in the state of technology the invention concerns a process for the refinement of molten steel in a converter with top blown oxygen on the molten steel surface with a water cooled blowing lance made up of a xe2x80x98shaftedxe2x80x99 lance body and a lance head.
Furthermore, the invention concerns a water cooled oxygen blowing lance made up of a shafted lance body and lance head, for implementation of this process more specifically, with an oxygen supply that runs through the lance body and flows to blowing nozzles distributed in the lance head and with outlet and inlet passageways for water running through the lance body to the cooling chambers in the lance head.
The invention is based on the task of achieving a process as above with which the metallurgical blowing process is monitored and controlled. The invention is also based on the task of creating an oxygen blowing lance that to a great extent is protected from the release of water.
According to the process, the problem is solved in that the temperature in the lance head of the blowing lance, which is transferred from the molten steel to the lance head is monitored using at least one of the temperature probes which are integrated into the lance head and regulated by cooling off with water and/or with an oxygen supply and/or the addition of aggregates and/or the distance of the lance head from the molten metal bath, In the process, the abrasion on the front end of the lance head as a function of the tool life and the temperature curve as a function of the tool life can be primarily considered as correction sizes. With the addition of aggregates it can be assumed that the rate and the time of the addition influence temperature regulation. In particular, scrap for cooling, briquettes, ores, lime and other similar things are considered as aggregates.
In the invention the temperature of the melting bath surface radiating directly onto the front end of the lance head is detected through the temperature in the lance head. Using this measurement of the temperature the metallurgical process of the refinement can be controlled. At the same time the head of the blowing lance can be protected from the release of water through the various individual steps or through a combination of measures.
It is true that it is already known how to determine temperature for water cooled blowing lances (JP 62-278217 A) in the treatment of enamels but such a blowing lance is used in another process and with other objectives. In this process the blowing lance is actually submerged in the enamel and the level of the slag of the molten metal relative to the blowing lance is determined by temperature probes which are staggered inside the lance body. In this known process though, protection from overheating by detecting the temperature of the lance and controlling the treatment process are not dealt with.
With the oxygen top blowing lance the above task is solved by integrating at least one temperature probe in the lance head behind its front end and between the cooling chambers, the signal lines of which are ducted through the lance body.
With the invention the temperature of the local area in the lance head can be determined, and from experience used as an indicator of the danger of rupturing. Thus there is a requirement for an immediate reaction to imminent collapse whether it be due to the outside wall of the lance head being too thin or becoming too weak.
In order to be able to mount the signal lines of (lie temperature probes simply and to be able to protect them they are in a central, protective pipe. This pipe should not have any connection to the process medium oxygen or to the cooling medium water. This is thus particularly advantageous and contributes to the reliability of operation if the head of the lance is burned down to the temperature probes integrated within it and is therefore open. In this situation it is therefore impossible for there to be a leak of oxygen and/or cooling water. In a preferred set tip the oxygen piping is situated in the middle of the lance head and surrounded with inlet and outlet channels for the cooling water through the formation of coaxial ring channels, where the outermost ring channel is the outlet channel and the center ring channel is the inlet channel.
In order to make the assembly work required when switching out a deteriorated lance head for a new one as easy as possible the temperature probe can be put in a bore hole of a nose saddle of the lance head using a disconnectable adapter which is secured inside the lance head. To ensure an error free measurement of temperature it is advantageous for the temperature probe to be kept in contact with the floor of the bore hole by a spring so that it can conduct heat.
For technical assembly reasons as well as for length compensation with various thermal linear expansions of the protective tube and the oxygen pipe, the protective pipe should overlap and seal the adapter like a telescopic sleeve.
In the blowing process the most extreme thermal damage to the oxygen blowing lance is sustained by the lance head. As a result the head of the oxygen lance is subjected to the most wear and tear and should be interchangeable. In order to make it easier to change out the lance head one of the set ups of the invention provides for there being coaxial fittings at the cooling chambers of the lance heads for continuing coaxial inlet and outlet cool water channels. These fittings may then be welded on to the continuing coaxial inlet and outlet channels.